1. Field of the Invention
This invention relates to improvements in variable speed torque transmitting coupling devices and more particularly, but not by way of limitation, to a variable fan for air cooled heat exchangers.
2. Description of the Prior Art
The usual presently available air cooled heat exchangers comprise a relatively large fan, for example a fan having blades which inscribe a 12 foot diameter circle, for moving air of ambient temperature across the heat exchanger coils, or the like. Most of the industrial type air cooled heat exchangers are designed to perform at the full load conditions, or at least near the full load conditions required for the highest ambient temperature that will occur during the hottest days of the year wherein the apparatus is to be utilized. As a consequence, the users of this type equipment in the southern gulf coast areas of this country normally specify equipment design for ambient temperatures of 95.degree. F., and 100.degree. F. in the broad middle band of the country, and 95.degree. F. in the northern parts of the country. When a particular design specification or criteria has been set, the only thought given to the flow of air passing through the exchanger bundle is to restrict the air flow to accomplish temperature control on the tube side of the exchanger. This control is to prevent over cooling when the ambient or air temperature is less than that for which the heat exchanger is designed. As a consequence, the heat exchanger fan, which normally is in operation 24 hours a day and 7 days a week, runs at full capacity continuously, regardless of the air temperature, thus expending optimum horsepower, which results in a great waste of energy.
A study has been made of the air temperature patterns at 25 locations in the United States, and as a result of these studies, it has been ascertained that ambient temperatures are much less than the anticipated maximum temperatures a large percentage of the time, and the heat exchanger fans may be operated at greatly reduced speeds a substantial amount of the operating time of the heat exchangers without reducing the cooling efficiency, thus conserving great quantities of energy.